1. Field of the Invention
The present invention relates to a method for manufacturing a solid lubricant film for a coated cutting tool including a drill, an end mill or a tap, having a substrate made of a tool steel, a high-speed steel, a cemented carbide, a cermet or a ceramic and being coated with a hard material including any one of TiN, TiCN, or TiAlN, or combinations thereof to improve a lubricant property of the cutting tool.
2. Description of the Related Art
Conventionally, a physical vapor deposition technique including an ion-plating is commonly used as a method for manufacturing a coated cutting tool. The main purpose thereof is to deposit on the cutting tool a coated film of a hard material including TiN, TiCN, TiAlN, and CrN. On the other hand, to improve a lubricant property of the cutting tool, a Japanese patent publication No. 09192908 published on Jul. 29, 1997, for example, discloses a dry lubricant coating film consisting mainly of molybdenum disulfide and fluorocarbon as main components, or that of consisting of graphite. These dry lubricant coating films are utilized by depositing or by wet-plating technique of lubricant powder, or by mold pressing, on portions of rotating parts.
A widespread of coated cutting tools in recent years resulted an improvement in manufacturing efficiencies as well as reductions of machining costs in metal cutting fields. These are achieved from the fact that coated materials are hard metals improving a wear resistance of the coated cutting tool.
On the other hand, the dry lubricant coating film consisting mainly of molybdenum disulfide and fluorocarbon as disclosed in the above publication No. 09192908, when applied to the cutting tool, will soon be removed from the surfaces of the cutting tool during machining work. To keep a long lubricant effect on the cutting tool, these dry lubricant coating film must be applied every time the cutting tool is used.
An object of this invention is to provide a solid lubricant film which has a very low frictional coefficient and improves a lubricant property of a coated cutting tool and a method for manufacturing the same for the coated cutting tool including a drill, an end mill or a tap, having a substrate made of a tool steel, a high-speed steel, or a cemented carbide, a cermet or a ceramic and being coated with a hard material film including any one of TiN, TiCN, or TiAlN, or combinations thereof.
Another object of this invention is to provide a solid lubricant film and a method for manufacturing the same for a coated cutting tool which has a long service life that stay sharp.
These and other objects are achieved by such a solid lubricant film and such a method for manufacturing the same for a coated cutting tool including a drill, an end mill or a tap, having a substrate made of a tool steel, a high-speed steel, a cemented carbide, a cermet or a ceramic and being coated with a hard material including any one of TiN, TiCN, or TiAlN, or combinations thereof. The method for manufacturing the solid lubricant film comprises: depositing on the coated cutting tool a solid lubricant oxide film (MOx: 0.2 xe2x89xa6xc3x97 less than 2) including an Oxygen as a main ingredient and metal M consisting of any one of Si, Zr, Ni, Fe, Co and Cr or combinations thereof; the thickness (t) of the solid lubricant oxide film being 0.01 xcexcmxe2x89xa6t less than 2.0 xcexcm. The solid lubricant oxide film is deposited on the coated cutting tool under conditions; heating a vacuum ion-plating chamber from room temperature to a temperature of between from 150xc2x0 C. to 450xc2x0 C.; and depositing the solid lubricant oxide film by an ion-plating by applying a negative bias voltage charge of a direct current of from xe2x88x9215 V to xe2x88x921000 V or by applying a high frequency alternating current having an effective negative bias voltage charge equivalent to those of the direct current of from xe2x88x9215 V to xe2x88x921000 V.
By such arrangements, by forming such metal oxide coating film on the coated cutting tool, the appropriate solid lubricant film has a very low frictional coefficient and improves a lubricant property of the coated cutting tool, and further, it greatly lengthens the service life that stay sharp of the coated cutting tool. Since such metal oxide coating film has the very low frictional coefficient, it greatly improves its lubricating property as compared with the above described conventional dry lubricant coating film consisting of molybdenum disulfide and fluorocarbon. However, if a metal oxide coating film has a too little frictional coefficient, it is prone to induce a chipping or a breakage of the chip of the coated cutting tool. Therefore, there are no saying that xe2x80x9cthe lower the frictional coefficient, the better metal oxide coating filmxe2x80x9d.
More specifically, generally speaking, although a coated cutting tool has a property to reduce a frictional coefficient thereof as compared with an uncoated cutting tool, in order to enhance an anti-condensability of the work material, it is appropriate to form a metal oxide film on the coated cutting tool. However, since most metal oxide form a dielectric insulator and commonly deposited via a chemical vapor deposition (CVD) technique, and further, to enhance its lubricant property of the coated cutting tool, it is generally formed rather thicker, resulting to be not appropriate as a cutting edge of a cutting tool. In case a metal oxide film is formed using conventional CVD technique generally formed in a high temperature, it is hard to repeat coating application on the metal oxide film. Since such metal oxide film has a good metallurgical bond with the base coating film, the metal oxide film is prone to cause to be removed together with the base coating film of the cutting tool as a whole, or only the upper lubricant metal oxide film is removed. Therefore, to coat the upper lubricant metal oxide film, it is essential to control its coating process.
To enhance a lubricant property of the lubricant oxide film for the coated cutting tool of this invention, the appropriate lubricant oxide film and the method for manufacturing the same is specified as using the ion-plating under conditions as set forth in claim 1. The reason the claim 1 specifically restricted the process data will be given below.
Wherein, the ion-plating under the temperature of the vacuum ion-plating chamber less than 150xc2x0 C. results that the deposited lubricant oxide film has a poor adhesion with the coated cutting tool, on the other hand, in case that temperature exceeds 450xc2x0 C., the deposited lubricant oxide film becomes friable, therefore the temperature of the vacuum ion-plating chamber is limited to range between from 150xc2x0 C. to 450xc2x0 C. The ion-plating by applying a negative bias voltage charge of a direct current less than xe2x88x9215 V does perform an insufficient reaction with the Oxygen and do not generate a good lubricant oxide film, on the other hand, in case that negative bias voltage charge exceeds or lower than xe2x88x921000 V, via an ion bombardment effect usually introduced in the ion-plating process, the reaction with the Oxygen becomes excessive or do not generate a lubricant oxide film, therefore, the negative bias voltage charge applying in the ion-plating is limited to range from xe2x88x9215 V to or a high frequency alternating current having an effective negative bias voltage charge equivalent to those of the direct current of from xe2x88x9215 V to xe2x88x921000 V. And the thickness (t) of the solid lubricant oxide film less than 0.01 xcexcm does not perform a purported effect, and that of over 2.0 xcexcm is liable to cause a chipping or pealing of the lubricant oxide film, the thickness (t) is limited to range 0.01 xcexcm less than t less than 2.0 xcexcm.
Preferably, the solid lubricant oxide film similarly enhances the lubricant property may be plated through the wet plating technique including a thermal oxidization, an anode oxidization or a steam-treatment technique as set forth in claim 2, wherein, since the thickness (t) of such solid lubricant oxide film less than 0.01 xcexcm does not perform a purported effect, and that of over 3.0 xcexcm is liable to cause a chipping or peeling of the lubricant oxide film, the thickness (t) of the solid lubricant oxide film via a steam-treatment technique is limited to range 0.01 xcexcmxe2x89xa6t less than 3.0 xcexcm.
Any one of the solid lubricant oxide films plated according to the present invention has a high adhesion with its base hard material coating film of the coated cutting tool as been shown in FIG. 1(a). Wherein in an indentation generated by an impression of an A-scale Rockwell hardness tester on the solid lubricant oxide film being observed in an optical sight of a microscope of one hundred magnifications no peeling or no obvious cracking between the substrate and the solid lubricant oxide film or between the substrate and the base or lower hard material film in an area extending over 1 mm from the periphery of the indentation. Claim 3 limits such criterion of judging grade of the adhesion with its base or lower hard material coating film. As compared with those of plated according to the conventional coating method shown in FIG. 1(b), it has a low adhesion with its base hard material coating film. In order to have a high adhesion with its base coating film, it is effective to coat a solid lubricant oxide film of the present invention which has the same or lesser hardness than that of the base hard material coating film.
FIGS. 2(a) and 2(b) illustrate enlarged partial sectional views of solid lubricant oxide films of the present invention in which it will be observed that a lubricant property of the upper solid lubricant oxide film according to the present invention is effected through a high bondability between a rough or defective porous surface of the base or lower hard material film and residual oxides of the solid lubricant oxide film thereon.